Cloths for electrochemical diaphragms and method of preparing same



Patented Feb. 22, 1944 ICE CLOTHS FOR ELECTROCHEMICAL DIA- PHRAGMS ANDMETHOD SAME OF PREPARING Karl Weber and Georg Bode, Gersthofen, nearAugsburg, Germany; vested in the Alien Property Custodian No Drawing.Application July 22, 1940, Serial No.

346,872. In Germany July 21, 1939 Claims.

(Granted The present invention relates to cloths for electrochemicaldiaphragms.

Various processes are already known for using filter cloths whichconsist of after-chlorinated polyvinyl chloride as diaphragms forelectrochemical purposes. It has, however, been found that in thepresence of a strongly acid electrolyte of an oxidizing action thetissue is not sufliciently tight so that even after shrinkage of thefiber in hot water of 90 C. the diffusion between the anode liquid andthe cathode liquid is not prevented.

Now we have found, and this is surprising, that felt or tissue of fibersfrom after-chlorinated polyvinyl chloride possess the desiredimpermeability which have been impregnated with silicic acid and atleast one water-insoluble inorganic salt. Insoluble salts of calcium andbarium are particularly suitable for that purpose. The impregnation may,for instance, be produced by saturating the felt or tissue with aqueoussolutions of salts of silicic acid and with metal salts,

for instance barium salts and after-treating them with dilute sulfuricacid.

The after-chlorinated polyvinyl chloride is for instance obtainedaccording to the process described in U. S. Patent No. 1,982,765.

The following examples serve to illustrate the invention, but they arenot intended to limit it thereto, the parts being by weight:

(1) After-chlorinated polyvinyl chloride (for instance felt 300/2) isplaced for 2 minutes into hot water of 90 C. After drying the shrinkedcloth is coated with an intimate mixture of 2 parts of barium sulfateand 1 part of waterglass (commercial) and allowed to dry in the openair.

The cloth is then treated with sulfuric acid of about per cent strengthand again dried in the open air: the diaphragm is then ready for use.

(2) After-chlorinated polyvinyl chloride (for instance felt 300/2) isplaced for 2 minutes into 'hot water of 90 C. The shrinked cloth isimpregnated with a barium chloride solution which has been saturated inthe hot condition. The cloth is then allowed to drop off and treatedwith dilute sulfuric acid for causing the barium sulfate to precipitate.After drying the cloth is soaked with water-glass and the silicic acidis set free by means of dilute sulfuric acid. After havingbeen dried inthe open air the diaphragm is ready for use.

(3) After-chlorinated polyvinyl chloride (for instance felt 300/2) isplaced for 2 minutes into hot water of 90 C. The shrinked cloth isimpregnated with calcium chloride solution and calcium phosphate isprecipitated on the fiber by means of tri-sodium phosphate. The cloth iswashed for a short time with water forremovinlthosodiumchlcriduitisthenloakedwith under the provisions of sec.14, act of March 2, 1927; 357 0. G. 5)

commercial waterglass and the silicic acid is set free with phosphoricacid. After having washed it with water and subsequently dried in theopentreating the impregnated cloth with an acid havair the diaphragm isready for use.

We claim:

1. Filter cloths for electrochemical diaphragms which are tight in thepresence of strongly acid electrolytes of an oxidizing action consistingof shrunk felted fibers of after-chlorinated polyvinyl chlorideimpregnated with silicic acid and at least one water-insoluble salt of ametal of the group consisting of calcium and barium.

2. Filter cloths for electrochemical diaphragms which are tight in thepresence of strongly acid electrolytes of an oxidizing action consistingof shrunk felted fibers of after-chlorinated polyvinyl chlorideimpregnated with silicic acid and barium sulfate. 3. Filter cloths forelectrochemical diaphragms which are tight in the presence of stronglyacid electrolytes of an oxidizing action consisting of shrunk feltedfibers of after-chlorinated polyvinyl chloride impregnated with silicicacid and calcium phosphate.

4. A process for producing filter cloths for electrochemical diaphragmsthat are tight in strongly acid electrolytes of an oxidizing actionwhich comprises subjecting toshrinkage felted fibers consisting ofafter-chlorinated polyvinyl chloride and impregnating the shrunk fiberswith a water insoluble salt of a metal selected from the classconsisting of barium and calcium and with an aqueous solution ofanalkali metal silicate and freeing silicic acid from the silicate by 'ingan anion corresponding to the anion of said water insoluble salt.

5. A process for producing filter cloths and electrochemical diaphragmsthat are tight in strongly acid electrolytes of an oxidizing actionwhich comprises subjecting to shrinkage fibers consisting ofafter-chlorinated polyvinyl chloride,

impregnating the shrunk fibers with a water soluble salt of a metalselected from the class consisting of barium and calcium, treating thethus impregnated cloth with an aqueous solution of a compound having ananion adapted to form a water insoluble salt with the aforementionedwater soluble salt to thereby produce in said fibers

